Tropical Storm GABRIELLE

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TROPICAL STORM GABRIELLE DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL072007
500 PM EDT SAT SEP 08 2007
AFTER BEING BRIEFLY INVOLVED WITH THE CIRCULATION CENTER THIS
MORNING...THE CONVECTION HAS SPENT MOST OF THE DAY QUITE SEPARATED
FROM THE CENTER...AND THE BAND IN THE NORTHEASTERN QUADRANT HAS
DISSIPATED. RECENTLY...HOWEVER...THE CIRCULATION CENTER AND THE
REMAINING CONVECTION IN THE NORTHWESTERN QUADRANT ARE IN THE
PROCESS OF BEING REUNITED. GABRIELLE HAS TAKEN ON MORE OF
THE APPEARANCE OF A SHEARED TROPICAL CYCLONE...AND BOTH AMSU AND
AIRCRAFT DATA SUGGEST THERE IS A WEAK WARM CORE...SO GABRIELLE IS
BEING DESIGNATED AS A TROPICAL STORM ON THIS ADVISORY. MAXIMUM
WINDS FROM THE AIR FORCE PLANE AT THE FLIGHT-LEVEL OF ABOUT 1000 FT
WERE ONLY 39 KT...EVEN WITHIN THE CONVECTION IN THE NORTHWESTERN
QUADRANT. GIVEN THOSE DATA AND THE OVERALL LESSENING OF THE
CONVECTIVE DEPTH AND COVERAGE...THE INTENSITY IS LOWERED TO 35 KT.
THE CURRENT SOUTHEASTERLY SHEAR MIGHT STILL LESSEN TEMPORARILY
TONIGHT...BUT WILL INCREASE FROM THE NORTH TOMORROW. THAT WINDOW
OF OPPORTUNITY FOR STRENGTHENING IS THE BASIS FOR THE OFFICIAL
FORECAST TO STILL CALL FOR SLIGHT STRENGTHENING. THE NEW FORECAST
IS LOWERED COMPARED TO THE PREVIOUS ADVISORY...CALLING FOR
GABRIELLE TO REACH ONLY 45 KT NEAR THE COAST OF NORTH
CAROLINA...AND THIS IS CONSISTENT WITH MOST OF THE GUIDANCE.
LITTLE CHANGE IN STRENGTH IS FORECAST ONCE GABRIELLE TURNS
NORTHEASTWARD AND EVENTUALLY BECOMES EXTRATROPICAL.
THE EXPOSED CIRCULATION CENTER IS EASY TO FIND...BUT THE SMALLER
SWIRL THAT APPEARS TO BE THE CENTER ON SATELLITE IMAGERY SEEMS TO
HAVE ROTATED ABOUT A LARGER MEAN CENTER DURING THE DAY. THE MOTION
OF THE MEAN CENTER IS NORTHWESTWARD AND SLOWER THAN BEFORE...OR
ROUGHLY 320/7. THE OFFICIAL TRACK FORECAST AND SUPPORTING
REASONING HAVE NOT NOTICEABLY CHANGED...WITH GABRIELLE EXPECTED TO
ROTATE AROUND THE WESTERN ATLANTIC RIDGE AND INTO THE MIDLATITUDE
WESTERLIES DURING THE NEXT COUPLE OF DAYS...PASSING NEAR OR OVER THE
OUTER BANKS OF NORTH CAROLINA ALONG THE WAY IN 24-36 HOURS. THE
NEW FORECAST ALSO CALLS FOR GABRIELLE TO BE ABSORBED BY A LARGER
SYSTEM OVER THE NORTH ATLANTIC BY 120 HOURS.
FORECAST POSITIONS AND MAX WINDS
INITIAL 08/2100Z 32.4N 74.7W 35 KT
12HR VT 09/0600Z 33.2N 75.4W 40 KT
24HR VT 09/1800Z 34.6N 75.8W 45 KT
36HR VT 10/0600Z 36.0N 74.8W 45 KT
48HR VT 10/1800Z 37.6N 72.8W 45 KT
72HR VT 11/1800Z 41.5N 65.5W 45 KT...BECOMING EXTRATROPICAL
96HR VT 12/1800Z 46.0N 55.0W 45 KT...EXTRATROPICAL
120HR VT 13/1800Z...ABSORBED BY LARGER EXTRATROPICAL SYSTEM
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FORECASTER KNABB
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